In my big box of cables I have, among other things, a double-ended USB-A cable. I understand that this is absolutely not standards compliant, and I have absolutely no idea of where I got it from. I have never used it. But it is a thing that exists.
Getting rid of almost 10 different proprietary charging cables for pre-smart phones and some old laptops felt great though :P
You and the other responders are probably familiar with it, but you made me look up this decent StackExchange answer again, coming from a search for "the forbidden usb cable" :)
I had one of those to charge a bicycle headlight. I gave it away with the bicycle, but in the span of time I had it, one visiting guest borrowed it to recharge a portable generic USB battery pack. So there you go, two product categories known to use that sort of cable!
I installed some HP slide-out rackmount keyboard/monitor units that used these as the host connection. This was back in the days when PS/2 was still around so they usually weren't used.
mine had 2 male USB ends on one side and 1 on the other. It was to power a laptop hard disk drive from USB if one port couldn't provide enough power. Feels illegal. I bought it off eBay with a money order in like 2003.
Getting rid of almost 10 different proprietary charging cables for pre-smart phones and some old laptops felt great though :P